1. Field of the Invention
The present invention generally relates to image display technique, and particularly relates to loading and unloading method and device for a cooling buffer in a precise length measuring machine.
2. The Related Arts
TTP (Total Pitch, inch long) precise length measuring machine is an important optical measurement apparatus in a TFT-LCD (Thin Film Transistor Liquid Crystal Display) manufacturing process. It is for the measurement of the total pitch when producing the first layer pattern of a TFT/CF (Color Filter) substrate by exposure. The total pitch measurement is achieved by measuring the interference pattern produced by the laser Michelson interference. The stability of laser is known to be susceptible to temperature variation. Therefore it is required that the TTP machine and the glass substrate to be measured have to be maintained at 23±0.1° C. Usually the TTP machine is kept in a room of constant temperature, and the glass substrate is loaded into a cooling buffer above the TTP machine first. After the glass substrate is cooled at a constant temperature it is then unloaded from the cooling buffer and mounted onto the TTP machine for measurement. If the cooling buffer fails to keep the glass substrate at the constant temperature or the temperature is different from that of the TTP machine, the thermal expansion and contraction effect to the glass substrate after it is mounted onto the TTP machine may affect the precision and reliability of the total pitch measurement. As such, a reliable and intelligent cooling buffer is required to the production of high-quality TFT/CF substrate.
Conventionally the cooling buffer of a TTP machine has four slots. The cooling buffer can be enabled or disabled, and a constant temperature interval can be configured (for the entire buffer, not for a particular slot). After the cooling buffer is activated, all empty slots are ready for loading sequentially. A loaded glass substrate, after being stored in a slot for the constant temperature interval, is unloaded by a robot and mounted onto the TTP machine for measurement. There is a disadvantage in the foregoing process.
The glass substrate in each slot is actually not held for the same cooling interval. Therefore, the glass substrates measured are of different conditions, leading to abnormal variance in the measurement results. This is due to the following problem. Let's assume that the cooling interval is 20 minutes, the measurement interval on the TTP machine is 10 minutes, and the four slots are loaded with four glass substrates sequentially (usually, there is a 30 seconds delay between two consecutive loadings, but this delay is ignored and the glass substrates are assumed to be loaded simultaneously). After the cooling interval for the glass substrate in slot 1 expires, it is mounted onto the TTP machine first and is measured for 10 minutes. Then the glass substrate in slot 2 is mounted onto the TTP but the glass substrate in slot 2 has already been in the cooling buffer for 20+10=30 minutes. Similarly, the glass substrates in slots 3 and 4 will be held for 40 and 50 minutes. In other words, the four glass substrates are cooled for different amount of time. In real-life production environment, it is found that, due to the influence by the precision of temperature control (23±1° C.) and the baking process, a glass substrate will be measured differently if it is cooled in the cooling buffer from 0 to 40 minutes, and the measurement would be stable after it is cooled about 40 minutes later. However, due to the tact time of production line and the timeliness of measurement data, it is rare to set the constant temperature interval to be more than 40 minutes.
As described above, the industry requires a loading and unloading mechanism that can keep a uniform cooling interval for the glass substrates so as to enhance the measurement precision.